Method of improving the machinability and mechanical properties of a steel

ABSTRACT

The machinability and mechanical properties of a steel are simultaneously improved by adding to the molten steel a sodium oxysulphide and one or more of selenium, tellurium and bismuth. The oxysulphide is suitably introduced into the ladle and the selenium, tellurium and bismuth into the molten steel when it is in the ingot mould.

United States Patent 1191 Almand 1 Jan. 8, 1974 [54] METHOD OF IMPROVING THE 3,169,857 2/1965 Rathke et a1 75/123 AA MACHINABILITY AND MECHANICAL 3,152,889 10/1964 Holowaty 75/123 AA 3,574,606 4/1971 Edgar et a1 75/123 AA PROPERTIES OF A STEEL 1,959,758 5/1934 Graham et al 75/123 0 x [75] Inventor: Edouard Almand, Dunkerque, 2,204,283 6/1940 Potts et a1. 75/123 AA X Franc-e 2,272,277 2/1942 Ramsey et a1 75 123 G x 3,152,890 10/1964 Holowaty 75 123 AA Asslgneer creusot-Loire, r France 3,192,040 6/1965 Goda et a1. 75/123 AA x [22] Filed: May 7, 1971 [21] APPL N0; 141 414 Primary Examiner-L. Dewayne Rutledge Ma 8, 1970 France 7016776 [52] US. Cl 75/129, 75/58, 164/57 [51] Int. Cl. C22c 37/00, B22d 27/20 [58] Field of Search 75/58, 123 AA, 123 A, 75/123 G, 129, 126 M, 128 P;23/129, 136, 137; 164/55, 57

[56] References Cited UNITED STATES PATENTS 2,236,716 4/194] Morris 75/123 AA Foreign Application Priority Data Assistant Examiner-Peter D. Rosenberg AttorneyCameron, Kerkam & Sutton ABSTRACT 6 Claims, No Drawings METHOD or IMPROVING THE MACHINABILITY AND MECHANICAL PROPERTIES OF A STEEL This invention relates to a method of making steel having improved machinability.

It has long been known that an addition of sulphur and/or lead to steel improves its machinability while impairing its mechanical properties, more particularly its transverse resilience. More recently, it has been found that selenium and tellurium, like sulphur and lead, have a favourable effect on machinability, but the effects of an addition of selenium or tellurium on the mechanical properties of the steel are sometimes favourable and sometimes unfavourable.

It is also known that greater improvements in ma chinability are obtained by adding sodium sulphite than by adding stick sulphur, but this is accompanied by a diminution of the mechanical properties of the steel, particularly transversely.

We have now found that it is possible simultaneously to obtain a considerable increase in machinability and also no diminution, or even a slight improvement, in mechanical properties, by adding certain materials to molten steel.

According to the invention, there is provided a method of making steel which comprises adding to the molten steel a sodium oxysulphide and oneor more of selenium, tellurium and bismuth.

The preferred sodium oxysulphides are the sulphite (Na SO the hyposulphite (Na s o land the metabisulphite (Na S O It is also possible to use the acid bisulphite (HNaSO although this is less advantageous.

Preferably, the addition of sodium oxysulphide to the steel is made in the ladle and the addition of selenium, tellurium or bismuth (or a mixture of two or more thereof) is made in the ingot mould.

The total amount of selenium, tellurium and bismuth is preferably less than 0.060 percent, particularly from 0.015 percent to 0.025 percent. Preferably, the amount of tellurium is not greater than 0.020 percent.

It has been found that addition of the sodium oxysulphides to steels promotes the formation of globular sulphides on solidification of the steels, the globules being distributed finely and homogeneously in the metal, and that selenium, tellurium and bismuth also promote this tendency to globulisation of the sulphides. However, the effect of the combined addtion of sodium oxysulphides and selenium, tellurium or two on the globulisation of the sulphides is very much greater than the sum of the individual effects of these wo types of addition, as is demonstrated below. c H v Six samples are niolten stel of tlie grade XC 42, containing 0.42 percent C and 0.025 percent S, were taken and various additions were made as set out below:

sulphur in the ladle and Table Continued Sample Analysis selenium in the ingot I mould: S 0.079% Se 0.018%

(f) the addition of sodium sulphite in the ladle and the addition'of selenium in the ingot mould: S 0.079% Se 0.020%

These ingots were rolled into billets of mm side, which were normalised and then turned into 60 mm diameter round bars. Turning tests on these round bars were carried out using high speed steel tools of the following composition:

C 0.80%; W 18%; Co 5%; V 1.10%; Mo 0.9%.

These turning tests were carried out without lubrication, with a cutting depth of 1 mm, a feed of 0.3 mm per revolution and a speed of 60 metres per minute. The tool cutting lives until put out of operation or burnt out were as follows:

Thus the tool life is multiplied by l.2from (a) to (b), and by 2.8 from (a) to (d). Thus one would normally expect the tool life (f) to be 1.2 X 2.8 3.35 times that of (a). In fact it is 4.9 times that of (a). t

This considerable improvement of machinability is due to a combination of the effects of the two types of additions. Also, the invention does not simply combine the individual effects of sulphur and selenium since sample (e) (stick sulphur and selenium) has a tool life only 3.9 times that of (a) whereas sample (f has a tool life 4.9 times that of (a).

It is also possible to improve the mechanical properties of the steel, more particularly transversely, by the method of the invention. For example, the following Table shows the values for the longitudinal resilience (KCU-L) and transverse resilience (KCU-T) given in the French standard specifications, in kgm/cm for the various ingots mentioned above:

oxysulphide and an addition 0 selenium:

Thus, longitudinally there is an improvement in the resilience in every case but the improvement is always small. The best result, however, is obtained with the steel according to the invention.

Transversely, on the other hand, there is a distinct deterioration in resilience as a result of the addition of sulphur, whether in the form of stick sulphur or sodium oxysulphides. Selenium in a proportion of 0.020 percent improves the transverse resilience in every case, with or without the addition of sulphur, its relative effect being practically the same with or without added sulphur, i.e., the transverse resilience is multiplied by 1.8 approximately in both cases.

Finally the L/T ratio of the reference steel is practically maintained in the steel according to the invention while it is greatly increased in the sulphur steels without selenium (cases and d).

Such improvements both as regards machinability and resilience are obtained with selenium contents as low as 0.020 percent for example.

Of course, variants or improvements as to detail are possible without departing from the scope of the invention, and the same applies to the use of equivalent means. For example, very advantageous results can also be obtained if the selenium addition is replaced by an addition of sodium oxyselenide.

I claim:

l. A method of improving the machinability and mechanical properties of a steel which consists essentially of adding to the molten steel in the ladle a sodium oxysulphide and adding at least one element selected from the group consisting of selenium, tellurium and bismuth to the molten steel in the ingot mold, the total amount of selenium, tellurium and bismuth added to the steel being less than 0.060 percent.

2. A method according to claim 1 wherein the sodium oxysulphide is selected from sodium sulphite, sodium hyposulphite and sodium metabisulphite.

3. A method of making steel which consists essentially of adding to the steel, while it is molten and in the ladle, a sodium oxysulphide and adding to the molten steel in the ingot mold from 0.015 to 0.025 percent in total of at least one element selected from the group consisting of selenium, tellurium and bismuth, tellerium being not greater than 0.020%.

4. A method according to claim 3 wherein the selenium is added to the steel as sodium oxyselenide.

5. A method according to claim 3 wherein the sodium oxysulphide is selected from sodium sulphite, sodium hyposulphite and sodium metabisulphite.

6. A method of improving the machinability and mechanical properties of a steel which consists essentially of incorporating in the steel, whilst it is molten, sodium sulphite in the ladle and selenium in the ingot mold, and allowing the steel to cool whereby globules of sulphides are finely and homogeneously distributed throughout the steel. 

2. A method according to claim 1 wherein the sodium oxysulphide is selected from sodium sulphite, sodium hyposulphite and sodium metabisulphite.
 3. A method of making steel which consists essentially of adding to the steel, while it is molten and in the ladle, a sodium oxysulphide and adding to the molten steel in the ingot mold from 0.015 to 0.025 percent in total of at least one element selected from the group consisting of selenium, tellurium and bismuth, tellerium being not greater than 0.020%.
 4. A method according to claim 3 wherein the selenium is added to the steel as sodium oxyselenide.
 5. A method according to claim 3 wherein the sodium oxysulphide is selected from sodium sulphite, sodium hyposulphite and sodium metabisulphite.
 6. A method of improving the machinability and mechanical properties of a steel which consists essentially of incorporating in the steel, whilst it is molten, sodium sulphite in the ladle and selenium in the ingot mold, and allowing the steel to cool whereby globules of sulphides are finely and homogeneously distributed throughout the steel. 